When I try to export a track as a .kml file I get an error message and the track is not exported. I choose Data > Tracks > Export to a Local File with format KML to '/storage/extSDCard/Pathaway' and then get an 'Error exporting' when I press 'OK'. Is there something I have failed to set correctly?

With KitKat (Android 4.4 or higher), Google has decided that it is a security breach for Apps to write to the External SD-Card. The only folder that PathAway is allowed to write to on the external card is its private location:
These are:
Express:
/Android/Data/com.muskokatech.PathAwayExp/files/

Pro
/Android/Data/com.muskokatech.PathAwayPro/files/

Hopefully this will get changed in the future, but for now its the best we can do.
Sorry.